Book excerpt: This book introduces the concept of hazards as part of the earth’s natural systems, in contrast to "disasters," which occur at the intersection of the built and natural environments. It emphasizes choices made by society that either increase or diminish our level of vulnerability to the impacts of hazards, and the role of the emergency manager in how these choices are made and acted upon. The book defines key concepts including mitigation, preparedness, resilience, vulnerability, and explains the role of the emergency manager in putting these principles into practice.